1. Field of the Invention
The present invention relates to phosphorus ylides and organic reaction schemes, and particularly to a method for making a phosphorous ylide, more particularly, 2,3-bismethoxycarbonyl-4-phenyl-5-arylhydrazono-cyclopenta-1,3-dienyltriphenylphosphonium.
2. Description of the Related Art
Phosphorus ylides are reactive compounds that take part in many valuable reactions of organic synthesis, e.g., the conversion of aldehydes and ketones into alkenes through a Wittig reaction. The development of simple synthetic routes for widely used organic compounds from readily available reagents is one of the major tasks in organic chemistry. Phosphorous ylides are most often prepared by the treatment of a phosphonium salt with a base. Most of the phosphonium salts are usually made from the phosphine and an alkyl halide, and they are also obtained by the Michael addition of phosphorus nucleophiles to activated olefins.
One such phosphorus ylide is 2,3-bismethoxycarbonyl-4-phenyl-5-arylhydrazono-cyclopenta-1,3-dienyl-triphenylphosphonium. The synthesis of 2,3-bismethoxycarbonyl-4-phenyl-5-arylhydrazono-cyclopenta-1,3-dienyl-triphenylphosphonium has been previously reported, but in impure form as one product of a mixture of products. Separation of the ylide from the mixture is very difficult. So there is a necessity to synthesize this compound in pure form, preferably using an easy way.
It has been previously reported that the addition of triphenylphosphine to dimethyl acetylenedicarboxylate 2 in dichloromethane by stirring at room temperature produced the intermediate A, which was followed by the addition of arylhydrazonals 1, leading to the direct formation of dihydropyridiazine-5,6-dicarbonates 3 (see Scheme 1, shown in FIG. 1).

On the other hand, when the addition of compound 1 to 2 is made under the normal conditions by stirring with dichloromethane at room temperature for some time, followed by addition of triphenylphosphine and continued stirring, the reaction furnished a mixture of two compounds (as examined by thin layer chromatography [TLC]). After separation and identification by elemental analysis and spectral data, it was found that one product was identified as compound 3 (40% yield), and other product was identified as compound 4 (60% yield) (see Scheme 2, shown in FIG. 2).
Separation of compound 4 (2,3-bismethoxycarbonyl-4-phenyl-5-arylhydrazono-cyclopenta-1,3-dienyl-triphenylphosphonium) from the mixture of compounds 3 and 4 proves to be very difficult, and the yield is poor.
The compound 2,3-bismethoxycarbonyl-4-phenyl-5-arylhydrazono-cyclopenta-1,3-dienyl-triphenylphosphonium is an intermediate in the production of cyclopentene derivatives, as in the following reaction scheme.
Cyclopentene derivatives are currently a matter of interest, since many have been found to have utility in inhibiting and treating tumors. See, e.g., U.S. Pat. No. 7,179,937, issued Feb. 20, 2007 to Gurjar et al. titled “Cyclopentanone Derivatives for Cancer Therapy.”
It is desirable to provide a synthesis scheme that produces the ylide in high yield in pure form. Thus, a method for making a phosphorus ylide solving the aforementioned problems is desired.